According to Sky Sports, the Chelsea squad used rugby tackle bags in training ahead of their match against Arsenal in order to improve their physicality.

According to reports, Chelsea adopted a slightly unusual training method ahead of the match, with players using rugby tackle bags to prepare for the physical pressure Arsenal may bring and the intense physical contests during set pieces.
The club is aware that a completely different kind of tough challenge awaits them this weekend. Arsenal have been in excellent form in recent seasons, especially in matches against Chelsea, where they have held the advantage. Chelsea are winless in their last nine Premier League meetings with Arsenal and have not left the Emirates Stadium with a victory for a full four years.